China has historically lagged behind on submarine capabilities. US officials say it's catching up. China's navy is moving toward all-nuclear submarine construction, the US Navy's intelligence lead said, describing a long-term shift in how Beijing builds its undersea force as it expands its capacity to produce more vessels in the coming decades.

Operating the world's largest navy by hull count, China possesses combat vessels -- including surface warships and submarines -- acquired from Russia decades ago, that helped it build sea power capable of challenging the United States.